Flux Measurements: In the immediate future, a few more experiments with tris-HCl buffered conditions are planned in order to confirm definitely the effects of HCO3- on Na ion transport. After that, the experiments with chloride and potassium isotopes are planned. In addition, the HCO3- transport will be elucidated. Ms. Ottilie Garsen will conduct the actual measurements. Microelectrode Measurements: The microelectrode experiments are planned to continue. Since we have definitive results from the sodium and ouabain experiments, the next step planned is to measure the intracellular potential as a function of a step reduction of (K ion) at the apical side of the endothelium. After that, the intracellular sodium and calcium activities will be measured. I have already obtained the Ca ions and Na ion-sensitive ligands from Dr. W. Simon of Switzerland. Ms. Gertrude Gunset will perform these experiments.